An M1A1 AIM or Abrams Integrated Management system is basically just a manufactured M1A1 or M1A1 "HA" that has been brought to a "like new" condition. In effect, it takes a tank built in the 1980s and brings it to a zero time/zero miles condition so it is like a tank that was built in the current year.
The "D" stands for digitized and signifies the addition of the computer applique package that brings an M1A1tank up to M1A2 standards as far as the integrated electronics that allow the tank commander to "see" all the other digitized tanks on the battlefield by looking at his display screen.
I hear that the Australians are not getting the depleted uranium armored M1A1s but the earlier ones. I do not know why not, but have surmised it could be for a few reasons:
1. We can't export that technology.
2. The Aussies may not want "radioactive" tanks.
3. It may make the tank too expensive.
4. They may feel they do not require the additional capability.
I do not know if any of the above are true, just my guess.